The Effect of Three Different Sensory Interventions (Mother’s Voice,Mother’s Milk,and Mother’s Holding) During Heel Lance on Pain Level in Term Newborns: A Randomized Controlled Trial

Abstract

Background:

Pain management is an important issue in newborns. This study aimed to compare the effects of three different sensory interventions (mother’s voice [hearing], mother’s milk smell [smell], and mother’s holding [touch]) during heel lance on pain levels in term newborns.

Methods:

In this randomized controlled trial, 120 term newborns included in the study were divided into four groups. Pain scores were assessed with Neonatal Infant Pain Scale during and after the procedure.

Results:

When compared in terms of interventions, newborns in mother’s voice and mother’s holding groups showed statistically significantly less pain response during the procedure compared with the control group (p = 0.005). But no significance was found in terms of mother’s milk smell.

Conclusion:

In conclusion, mother’s holding and mother’s voice are effective methods to reduce pain during heel prick procedure in newborns. In addition, both maternal smell and maternal touch may have had an effect in the mother’s holding group. Nevertheless, future studies with different designs on the effect of breast milk smell are recommended. (Trial registration: https://clinicaltrials.gov/study/NCT05526378.)

Introduction

Newborns are exposed to many painful procedures in the first hours of life. Due to the immature nervous system, the adverse effects of pain response are more common in newborns compared with adults. Furthermore, the damage caused by painful procedures may lead to structural and functional changes that may impact adulthood.¹ Therefore, pharmacological and nonpharmacological methods are used in pain management. The fact that pharmacological methods may adversely affect newborn health in the long term has made the use of nonpharmacological methods a more rational approach.^2,3 In the literature, it has been reported that methods such as kangaroo care, breastfeeding, swaddling, and oral sucrose administration reduce pain and provide relaxation in newborns.^4–7

Music and some sounds exert analgesic effects by providing sensory stimulation and are used in pain management in newborns.² According to a meta-analysis, pain scores were lower and vital signs were more stable in newborns who were made to listen to the mother’s voice during painful procedures.⁸ In a randomized controlled trial, pain levels decreased significantly in newborns who were made to listen to music during a painful procedure.⁹ Another study reported that newborns who were made to listen to the mother’s voice during the heel lance procedure behaved calmer and had lower pain scores.¹⁰

The sense of smell starts to develop during the intrauterine period, and some scents have soothing effects on newborns.¹¹ According to a meta-analysis, the mother’s milk smell has an analgesic effect in newborns.¹² A randomized controlled trial compared own mother’s milk smell and the smell of another mother’s milk. According to the study, both smells effectively reduced the pain.¹³ According to another study, although the smell of own mother’s milk reduced the pain, there was no decrease in pain levels in infants who were made to smell another mother’s milk.¹⁴

The fact that the mother and the infant are in contact with each other increases oxytocin levels and reduces cortisol levels in newborns.¹⁵ Mother’s holding is one of the methods used to reduce pain in newborns.^16,17 Mother’s holding ensures that the newborn feels comfortable and safe and reduces adverse reactions.¹⁸ In their study, Inal et al.¹⁷ concluded that pain scores were lower in newborns who were in their mother’s arms during the heel lance procedure.

Despite the presence of studies comparing various nonpharmacological methods used in pain management in newborns,^6,18,19 there is no study comparing three different senses with each other. This randomized controlled trial aimed to compare the effects of three different sensory interventions, including mother’s voice (hearing), mother’s milk smell (smell), and mother’s holding (touch), during heel lance on pain levels in term newborns.

Methods

Study design

The present study is a randomized, controlled experimental trial. The Clinical Trial Number (NCT05526378) was obtained prior to the start of the study (https://clinicaltrials.gov).

Population and sample

Newborns who were followed up in the baby’s room of a hospital in Turkey between December 2022 and May 2023 constituted the study population. The sample size of the study was determined based on studies in the literature investigating the effects of kangaroo care,²⁰ mother’s voice,²¹ and mother’s milk smell¹⁴ on pain level in newborns. When the sample size of the study was calculated using the program G*Power (3.0.10) with a power of 80%, a margin of error of 0.05, and an effect level of 0.27, it was found that 30 cases should be included in each group. Accordingly, it was determined that a total of 120 newborns should be included: 30 cases in the mother’s voice group, 30 cases in the mother’s milk smell group, 30 cases in the mother’s holding group, and 30 cases in the control group. Cases that met the study criteria were divided into four groups by randomization. Cases were randomly assigned to the groups using a simple random sampling program. Thus, a total of 120 newborns who met the study’s inclusion criteria and whose parents agreed to participate in the study were enrolled in the research. Cases continued to be included in the study until the target sample size was reached. The CONSORT flowchart was prepared in line with the CONSORT-SPI 2018 checklist (Fig. 1).²²

FIG. 1.

CONSORT-SPI 2018 flowchart.

Inclusion criteria:

Newborns born between 37 + 0/7–41 + 6/7 gestational weeks.

Newborns with compatible gestational age and birth weight.

Healthy newborns with stable vital signs.

Exclusion criteria:

Situations in which the mother and the newborn are not together (such as the newborn’s admission to the neonatal intensive care and early discharge of the mother).

Measurements

Descriptive information form

This form consisting of six items (sex, gestational week, birth weight, type of birth, 1- and 5-minute APGAR scores) was prepared in accordance with the literature and included the cases’ personal information.^23,24

Follow-up form

This form included information on the Neonatal Infant Pain Scale (NIPS) score 5 minutes before the procedure, the NIPS score during the procedure, and the NIPS score 5 minutes after the procedure.

Neonatal Infant Pain Scale

The NIPS, which was developed by Lawrence et al.,²⁵ was adapted to Turkish by Akdovan.²⁶ The scale assesses the newborn’s behavioral and physiological responses to pain.^25,26 In the assessment, 0–2 points refer to no pain, 3–4 points refer to mild or moderate pain, and >4 points refer to severe pain. Pain intensity increases with an increase in the total score that can be obtained from the scale.

Research process

An experienced baby nurse performed the heel lance procedure in accordance with the routine procedure in all groups, and the following steps were followed: 1.

The heel area where blood would be taken was wiped with alcohol gauze.

It was waited for the alcoholic solution to dry.

Blood was collected by the baby nurse by puncturing the area where blood would be taken with a lancet with a puncture depth of 1.2 mm.

After the procedure, minimum pressure was applied to the area where blood was taken for a short period to stop bleeding.

The heel lance procedure and nonpharmacological methods were performed by a single person to avoid differences between the interventions.

Mother’s voice group

An informed consent form and a voluntary consent form were presented to the parents of newborns who were planned to be included in the group, and their consent was obtained. Personal information of the newborns whose families gave consent was recorded using the Descriptive Information Form. The newborn was fed by his/her mother 1 hour before the heel lance procedure. The heel lance procedure was carried out in the mother–infant adaptation room, and no other patient or companion was present in the room during the procedure. Factors such as noise, excess light, and darkness were excluded during the procedure. Pain level was assessed for the first time using the NIPS, and the intervention was initiated with the newborn who received 0 points. Five minutes before starting the heel lance procedure, the mother started to call out to her infant at a sound level of 40–60 decibels. While the mother continued to call out to her infant, the heel lance procedure was initiated, and the pain level was assessed for the second time with the NIPS during the procedure. The mother continued to call out to her infant until the 5th minute after the heel lance procedure was completed. The pain level was assessed for the third time with the NIPS at the 5th minute, and the intervention (the mother calling out to her infant) was terminated. A Benetech Gm1352 model decibel meter was used to measure the sound level. All scores obtained from the NIPS were recorded in the Follow-up Form.

Mother’s milk group

An informed consent form and a voluntary consent form were presented to the parents of newborns who were planned to be included in the group, and their consent was obtained. Personal information of the newborns whose families gave consent was recorded using the Descriptive Information Form. The newborn was fed by his/her mother 1 hour before the heel lance procedure. The heel lance procedure was carried out in the mother–infant adaptation room, and no other patient or companion was present in the room during the procedure. Factors such as noise, excess light, and darkness were excluded during the procedure. Meanwhile, the pain level was assessed for the first time using the NIPS, and the intervention was initiated with the newborn who received 0 points. Just before starting the intervention (smelling the mother’s milk), the newborn’s mother was asked to express some breast milk (approximately 5 mL). The expressed breast milk was taken into a syringe and dropped enough to soak the entire 2.5 × 2.5 cm sterile gauze. Five minutes before the heel lance procedure, the gauze soaked with breast milk was placed close to the newborn’s nose wings. The gauze soaked with breast milk was kept in a position close to the newborn’s nose wings, starting from 5 minutes before the heel lance procedure and until 5 minutes after the procedure was completed. The pain level was assessed for the second time with the NIPS during the heel lance procedure. Pain level was assessed for the third time with the NIPS 5 minutes after the heel lance procedure, and the intervention (smelling mother’s milk) was terminated. All scores obtained from the NIPS were recorded in the Follow-up Form.

Mother’s holding group

An informed consent form and a voluntary consent form were presented to the parents of newborns who were planned to be included in the group, and their consent was obtained. Personal information of the newborns whose families gave consent was recorded using the Descriptive Information Form. The newborn was fed by his/her mother 1 hour before the heel lance procedure. The heel lance procedure was carried out in the mother–infant adaptation room, and no other patient or companion was present in the room during the procedure. Factors such as noise, excess light, and darkness were excluded during the procedure. The pain level was assessed for the first time using the NIPS, and the intervention was initiated with the newborn who received 0 points. Five minutes before the heel lance procedure, the mother took her infant in her arms and sat upright in a chair. The mother did not call her infant during the intervention and kept him/her in a fixed position. The intervention started 5 minutes before the heel lance procedure and continued until 5 minutes after the procedure was completed. The pain level was assessed for the second time with the NIPS during the heel lance procedure. The pain level was assessed for the third time with the NIPS 5 minutes after the heel lance procedure, and the intervention (mother’s contact) was terminated. All scores obtained from the NIPS were recorded in the Follow-up Form.

Control group

Randomization

The randomization method was used to divide the cases into three intervention groups and one control group. Numbers ranging from 1 to 120 were assigned to four groups using an online randomization program (randomizer.org). Thus, the randomization process was conducted completely randomly and independently. The following procedure was followed to assign cases to the groups: The first newborn included in the study was identified as Case 1. Then, each consecutive newborn included in the study was numbered, and their distribution into the groups was determined by randomization. The researcher performing the intervention (E.D.) and R.D. was aware of the distribution of cases into the groups due to differences in interventions. However, blinding was applied to the other researcher (H.D.K.) who analyzed quantitative data.

Statistical analysis

The SPSS 27.0 package program was used to analyze the data. While continuous data were presented with mean and standard deviation, categorical data were presented with frequency and percentage. The chi-square and Kruskal–Wallis H tests were performed to compare the participants’ descriptive characteristics. The Kruskal–Wallis H test was applied to compare the NIPS scores between the groups. Posthoc Bonferroni correction was applied for a further analysis of the significant data. In the analyses conducted, the level of significance was taken as p ≤ 0.05.

Ethical considerations

To conduct the study, written institutional permission from the hospital and ethics committee approval dated and numbered 2022/105 from Istanbul University-Cerrahpasa Clinical Research Ethics Committee were obtained. Additionally, verbal and written consent was obtained from the families of the newborns by explaining the procedures to be performed. The study was conducted in line with the principles of the Declaration of Helsinki.

Results

Table 1 contains the descriptive characteristics of the newborns. Accordingly, sex, delivery method, birth weight, gestational week, and 1-minute and 5-minute APGAR scores were similar in all groups (p > 0.05) (Table 1).

Table 1.

Comparison of the Groups’ Descriptive Characteristics

	Mother voice (n = 30)		Mother milk (n = 30)		Mother holding (n = 30)		Control (n = 30)		Test	p
	N	%	N	%	N	%	N	%	Test	p
Sex									χ²: 0.800	0.849
Girl	16	53.3	13	43.3	16	53.3	15	50
Boy	14	46.7	17	56.7	14	46.7	15	50
Type of birth									χ²: 5.278	0.153
Vaginal	10	33.3	9	30	15	50	15	50
Cesarean	20	66.7	21	70	15	50	15	50

	x̄ ± SS	Min-max	x̄ ± SS	Min-max	x̄ ± SS	Min-max	x̄ ± SS	Min-max
Birth weight	3094.2 ± 317.9	2,535–3,880	3067.9 ± 406.1	2,540–4,100	3082.8 ± 444.3	2,530–4,595	3263.3 ± 426.9	2,620–4,350	H = 5.044	0.169
Gestational weeks	38.1 ± 1.1	37–41	38.0 ± 0.9	37–40	38.7 ± 1.1	37–41	38.6 ± 0.9	37–41	H = 7.852	0.051
1-minute APGAR	8.1 ± 0.7	7–9	8.3 ± 0.6	7–9	8.3 ± 0.7	6–9	8.1 ± 0.5	7–9	H = 3.741	0.291
5-minute APGAR	9.2 ± 0.8	7–10	9.2 ± 0.6	8–10	9.4 ± 0.6	8–10	9.2 ± 0.4	9–10	H = 5.454	0.141

χ², chi-square; H, Kruskal–Wallis H.

Upon comparing the NIPS scores between the groups, newborns in the mother’s voice and mother’s holding groups displayed statistically significantly less pain response compared with the control group (p = 0.005). The NIPS score obtained during the procedure in the mother’s milk group was similar to that in the control group (p > 0.05). No significance was found between the groups in terms of the NIPS score taken 5 minutes after the procedure (p > 0.05) (Table 2).

Table 2.

Comparison of the Groups’ NIPS Scores According to Measurement Times

	Mother voice (n = 30) (a)		Mother milk (n = 30) (b)		Mother holding (n = 30) (c)		Control (n = 30) (d)		Test	p
	(x̄ ± SS)	Min-max	(x̄ ± SS)	Min-max	(x̄ ± SS)	Min-max	(x̄ ± SS)	Min-max	Test	p
NIPS score during the procedure	3.3 ± 1.4	1–7	3.4 ± 1.5	0–7	3.2 ± 1.0	1–5	4.5 ± 1.8	0–7	H = 12.896 (a, c < d)^a	0.005*
NIPS score 5 minutes after the procedure	0.5 ± 0.8	0–3	0.8 ± 1.4	0–5	0.5 ± 0.8	0–3	0.9 ± 1.3	0–5	H = 1.436	0.697

^aPost hoc Bonferroni test, *p < 0.05.

H, Kruskal–Wallis H.

NIPS, Neonatal Infant Pain Scale.

Discussion

The study is the first to investigate the effects of three different sensory methods on reducing heel lance pain. This study showed that interventions such as exposure to the mother’s voice and being in the mother’s arms during the heel lance procedure were more effective in reducing pain compared to routine care. No difference was observed between pain scores during the procedure between the mother’s milk smell group and the control group. No significance was found in terms of pain scores in all groups after the procedure.

Auditory interventions applied during the heel lance procedure in newborns effectively reduce pain.^27,28 The mother’s voice intervention is effective in reducing pain in newborns.²⁹ The mother’s voice helps the newborn feel safe and relaxed.³⁰ A meta-analysis study revealed that the mother’s voice was effective in reducing pain scores in preterm and term newborns.⁸ In another study, pain scores of newborns exposed to the mother’s voice during the heel lance procedure were found to be lower.²¹

Olfactory stimulation interventions consist of exposing the infant to a scent during a painful procedure. A meta-analysis study examining the effects of olfactory stimulation interventions applied during painful procedures on pain in newborns found that olfactory stimulation interventions performed with a familiar scent effectively reduced pain compared with routine care.³¹ In a meta-analysis study investigating the analgesic effects of breast milk smell on newborns, it was found that newborns who were exposed to breast milk smell had lower pain scores and cried for a shorter time compared with newborns who were not exposed to any smell. Newborns who were exposed to the mother’s milk smell were found to have lower salivary cortisol levels compared with newborns exposed to formula smell.¹² In newborns, the mother’s milk smell increases blood flow oxygenation in the orbitofrontal region more than the smell of formula. Thus, newborns can distinguish the smell of breast milk and formula milk.³² A study found that the pain scores of newborns who were exposed to their own mother’s milk were lower compared with newborns who were exposed to another mother’s milk.¹³ Results from two other studies similarly showed that newborns who exposed to breast milk odor during the heel lance procedure reported lower pain scores during and after the procedure.^33,34 In the present study, contrary to the general opinion in the literature, a statistical result similar to the control group was found in the mother’s milk group. Nevertheless, in a study comparing amniotic fluid odor, mother odor, and mother’s milk odor, it was reported that none of the odor interventions were effective in reducing pain.³⁵

Although the results of the current study showing that mother’s milk smell is not effective in pain management seem to contradict the general findings in the literature, there may be more than one possible reason for these differences. Study design, methodological differences, and the protocol used may play an important role in these results. In the present study, impregnation of breast milk odor in gauze and placing it on the wings of the nose may be different from the methods used in other studies. Insufficient odor intensity may have led to ineffective results. In the present study, the application of mother’s milk smell only 5 minutes before the painful procedure differs from the methods in the literature that are applied for a longer time or during the procedure.³⁶ The short exposure time may have prevented the analgesic effect from occurring. The effect of mother’s milk smell may vary according to the age, maturity level, and gestational age of newborns. For example, it should be considered that odor perception may be different in premature infants, and this may affect the results of the study. Instead of the “no odor exposure” groups used as the control group in some studies in the literature, the characteristics of the control group in the present study may be different.³⁷ This may lead to statistical differences. In addition, the type, duration, and severity of the painful procedure may also affect the effectiveness of mother’s milk smell. For example, shorter or less severe painful procedures may not be sufficient to demonstrate the effect of mother’s milk smell.

In the study, post-procedure pain scores of newborns who were in their mother’s arms were lower. Inal et al.¹⁷ found that infants who were in their mother’s arms during the heel lance procedure had lower pain scores. On the contrary, another study revealed that the pain scores of newborns who were in their mother’s arms during the heel lance procedure were higher. This result was associated with maternal stress.³³ The mother’s lap makes the newborn feel safe and comfortable, which reduces the level of stress and pain in the newborn and eliminates the adverse effects of painful procedures.³⁸ The mother’s lap can be used to reduce pain during the heel lance procedure.³⁹ Parental involvement in infant care is one of the basic principles of family-centered care. The importance of family-centered care in neonatal pain control is known.³⁹ The present study investigated the effects of three different sensory interventions applied by mothers on reducing pain. In the study, there was a statistically significant decrease in the NIPS score during and 5 minutes after the procedure in all interventions. Upon comparing the groups, the pain was less in the mother’s voice and mother’s holding groups compared with the control group not undergoing any intervention.

Conclusions

The study determined that listening to the mother’s voice or being in the mother’s arms during the heel lance procedure, which is a painful procedure, effectively reduced the pain level in newborns. Pain levels decreased in all newborns 5 minutes after the procedure, regardless of whether the intervention was performed or not. In this respect, the use of nonpharmacological methods during routine painful procedures in newborns is effective in providing pain management. It may be recommended to midwives and nurses in clinical practice to have the infant listen to the mother’s voice during the procedure or perform the procedure while the infant is in the mother’s arms. In addition, although mother’s milk smell was reported to reduce pain in studies on mother’s milk smell in the literature, it was not found to reduce pain in the current study. It is recommended that future studies should be designed taking into account the differences in the form of intervention.

Limitations

Since the researcher performing the interventions knew which group the cases were in, double blinding could not be performed. No nonpharmacological methods were used in routine care at the institution where the study was conducted. The results of the study are limited to the single center where the study was conducted. Moreover, the way interventions are implemented is limited only by the study design. Therefore, the study results cannot be generalized.

Footnotes

Authors’ Contributions

R.D. and E.D. conceived the idea, curated the data, performed the formal analysis, wrote the initial draft, and approved the final version. H.D.K. performed data curation and formal analysis and approved the final version. M.T. curated the data and approved the final version.

Disclosure Statement

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding Information

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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